Therapeutic Target In Inflammatory Bowel Disease Research Articles

Interleukin-21 (IL-21) Controls Inflammatory Pathways in the Gut

In both Crohn's disease (CD) and ulcerative colitis (UC), the major forms of inflammatory bowel diseases (IBD) in humans, the pathologic process consists of an aberrant local immune response to components of the bacterial microflora, due to abnormally strong effector cell activity that is poorly controlled by counter-regulatory mechanisms. There is also evidence that mucosal immune cells actively interact with non-immune cells to promote tissue damage, and that cytokines are essential mediators of this cross-talk. Interleukin-21 (IL-21), the latest member of the common gamma-chain-dependent cytokine family, is a product of activated CD4+ T cells and natural killer T cells. IL-21 is produced in excess in CD tissue, where it helps sustain the ongoing Th1 inflammation. High IL-21 production occurs also in the inflamed colon of most patients with UC, a disease that is not associated with a marked Th1 cell response. This suggests that, in the gut, IL-21 can modulate additional inflammatory pathways other than enhancing Th1 cell immunity. Indeed, IL-21 stimulates the secretion of extracellular matrix degrading enzymes by fibroblasts, and of the T cell chemoattractant, MIP-3 alpha, by epithelial cells. These data collectively indicate that IL-21 is a mediator of the chronic inflammatory response in CD and UC, and suggest that IL-21 may be an emerging therapeutic target in IBD.

13-Oxo-ODE is an endogenous ligand for PPARγ in human colonic epithelial cells

Background The ligand activated nuclear hormone receptor peroxisome proliferator-activated receptor gamma (PPARγ) induces transcriptional repression of pro-inflammatory factors. Activation of PPARγ is followed by amelioration of colitis in animal models of inflammatory bowel disease (IBD). A reduced expression of PPARγ was found in epithelial cells of patients with ulcerative colitis. The eicosanoids 13-HODE and 15-HETE are products of 12/15-lipoxygenase (LOX) and endogenous ligands for PPARγ. Dehydrogenation of 13-HODE by 13-HODE dehydrogenase results in formation of the 13-Oxo-ODE. Highest activity of 13-HODE dehydrogenase is found in colonic epithelial cells (CECs). We therefore investigated whether 13-Oxo-ODE is a new endogenous ligand of PPARγ in CECs. Methods LOX activity and 13-HODE dehydrogenase in CECs were investigated after stimulation with arachidonic or linoleic acid. LOX metabolites were identified by RP-18 reversed-phase HPLC. Binding of 14C-labelled 13-Oxo-ODE was demonstrated using a His-tagged PPARγ. Results Stimulation of HT-29 and primary CECs homogenates with and without Ca-ionophor was followed by the formation of high amounts of the linoleic acid metabolite 13-Oxo-ODE (155 and 85 ng/ml). The decrease of IL-8 secretion from IEC was more pronounced after pre-incubation with 13-Oxo-ODE compared to the PPARγ agonist troglitazone and higher as with the known PPARγ ligands 13-HODE and 15-HETE. Binding assays with 14C-labelled 13-Oxo-ODE clearly demonstrated a direct interaction. Conclusion High amounts of 13-Oxo-ODE can be induced in CECs by stimulation of linoleic acid metabolism. 13-Oxo-ODE binds to PPARγ and has anti-inflammatory effects. 13-HODE dehydrogenase might be a therapeutic target in IBD.

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Beyond Our Pages

Differential Angiogenic Regulation of Experimental Colitis

Inflammatory bowel diseases (IBDs) are chronic inflammatory disorders of the intestinal tract with unknown multifactorial etiology that, among other things, result in alteration and dysfunction of the intestinal microvasculature. Clinical observations of increased colon microvascular density during IBD have been made. However, there have been no reports investigating the physiological or pathological importance of angiogenic stimulation during the development of intestinal inflammation. Here we report that the dextran sodium sulfate and CD4+CD45RBhigh T-cell transfer models of colitis stimulate angiogenesis that results in increased blood vessel density concomitant with increased histopathology, suggesting that the neovasculature contributes to tissue damage during colitis. We also show that leukocyte infiltration is an obligatory requirement for the stimulation of angiogenesis. The angiogenic response during experimental colitis was differentially regulated in that the production of various angiogenic mediators was diverse between the two models with only a small group of molecules being similarly controlled. Importantly, treatment with the anti-angiogenic agent thalidomide or ATN-161 significantly reduced angiogenic activity and associated tissue histopathology during experimental colitis. Our findings identify a direct pathological link between angiogenesis and the development of experimental colitis, representing a novel therapeutic target for IBD.

No Evidence for an Involvement of the P38 and JNK Mitogen-Activated Protein in Inflammatory Bowel Diseases

Involvement of mitogen-activated protein (MAPK) in inflammatory bowel disease (IBD) remains enigmatic. We sought to evaluate the expression and activity of p38 and JNK MAPK in IBD and 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced colitis; and the effects of a p38 inhibitor, SB203580, in TNBS colitis. P38 and JNK were quantified in colonic mucosa of 28 IBD patients and 19 controls and in 77 TNBS or control mice treated or not with SB203580. Colitis severity was assessed by survival, macroscopic and microscopic scoring, and molecular markers. Expression and activity of p38 and JNK were similar in IBD patients and controls and not modified by inflammation. In mice, p38 and JNK expression or activity did not increase following the induction of colitis. SB203580 decreased the p38 activity but displayed no clinical nor biological therapeutic effect. In conclusion, these results minimize the role of p38 and JNK in inflammatory colitis and the interest of p38 as a therapeutic target in IBD.

Role of tumor necrosis factor receptors in an animal model of acute colitis

TNF-alpha is known to play an important role in inflammatory bowel disease (IBD); however, the pathophysiological role of its receptors is still under study. Acute colitis was induced in rats by intracolonic administration of trinitrobenzene sulfonic acid (TNBS). Control rats received the ethanol vehicle. Rats were sacrificed 72 h later and samples of tissue and fluids were collected. There was a significant increase in the protein levels of sTNF-alpha, sTNFRI, and sTNFRII in the peritoneal fluid (PF) of experimental rats. TNF-alpha, TNFRI, and TNFRII mRNA expression was increased significantly in the colon of experimental animals compared to controls. TRAF3 and TRAF5 expression was also significantly higher, as was that of the adhesion molecules ICAM-1 and E-selectin. The increased expression of TNF-alpha, TNFRs, and the associated signaling factors in the colon of this rat model of IBD provides further evidence for their involvement in the promotion of inflammation and tissue damage. In addition, increased levels of sTNFRs in the PF of experimental rats—particularly sTNFRII—may be involved in the development of colitis by serving as a reservoir of TNF-alpha, and thus provide a novel therapeutic target for IBD.

611 HCV infection is associated with a potent anti-apoptotic response in hepatocytes

TNF-alpha is known to play an important role in inflammatory bowel disease (IBD); however, the pathophysiological role of its receptors is still under study. Acute colitis was induced in rats by intracolonic administration of trinitrobenzene sulfonic acid (TNBS). Control rats received the ethanol vehicle. Rats were sacrificed 72 h later and samples of tissue and fluids were collected. There was a significant increase in the protein levels of sTNF-alpha, sTNFRI, and sTNFRII in the peritoneal fluid (PF) of experimental rats. TNF-alpha, TNFRI, and TNFRII mRNA expression was increased significantly in the colon of experimental animals compared to controls. TRAF3 and TRAF5 expression was also significantly higher, as was that of the adhesion molecules ICAM-1 and E-selectin. The increased expression of TNF-alpha, TNFRs, and the associated signaling factors in the colon of this rat model of IBD provides further evidence for their involvement in the promotion of inflammation and tissue damage. In addition, increased levels of sTNFRs in the PF of experimental rats—particularly sTNFRII—may be involved in the development of colitis by serving as a reservoir of TNF-alpha, and thus provide a novel therapeutic target for IBD.

Upregulation of Interleukin-12 and -17 in Active Inflammatory Bowel Disease

Background: Cytokines are essential mediators of the intestinal inflammation during active episodes of inflammatory bowel disease (IBD). Interleukin (IL)-12 and IL-17 are potent immunoregulatory cytokines whose roles in the pathogenesis of IBD are unknown. The aim of this study was to evaluate the colonic expression of IL-12 and IL-17 genes in IBD. Methods: Fifty-one patients (22 with ulcerative colitis (UC), 17 with Crohn disease (CD), and 12 controls) who underwent colonoscopy were included. IBD disease activity was determined using a clinical grading scale. The degree of inflammation, as well as the content of CD4+ T cells (synthesizing IL-17) and CD68+ macrophages (synthesizing IL-12) in colonic biopsies, was determined. The amounts of IL-12 and IL-17 mRNA were assessed by RT-PCR, using GAPDH as an internal standard. Results: In colonic specimens, IL-17 mRNA expression was increased in moderately and severely active UC (P = 0.03) and in all degrees of activity in CD (P < 0.04). Levels of IL-12 mRNA were upregulated in both active UC and active CD compared to controls (P < 0.02). In cases of remission, IL-12 mRNA expression was similar to that found in control samples. Compared to controls, histological examination showed significant differences in signs of chronic and acute inflammation in UC (P < 0.01) and CD (P < 0.02), revealing a high correlation between clinical disease activity and histological scoring (r 2 = 0.92, P < 0.005). Whereas CD4+ T cells were observed in lymphocyte aggregates located profound in the lamina propria, CD68+ macrophages were primarily found just underneath the surface epithelium. The density of CD4+ and CD68+ cells correlated significantly with the amounts of IL-17 and IL-12 mRNA, respectively (P < 0.05). Conclusion: The expression of both IL-12 and IL-17 mRNA is induced in active UC and CD and may thus be involved in sustaining the intestinal inflammation in IBD. Inhibition of IL-12 or IL-17 might be future therapeutic targets in IBD.

In brief

Tumour necrosis factor (TNF)-α has a central pathogenic role in inflammatory bowel disease (IBD). During local and systemic inflammatory reactions, membrane-bound TNF-α is cleaved extracellularly by a specific zinc metalloprotease, termed TNF-α-converting enzyme (TACE). This yields the soluble form of TNF-α that acts as a compartmentalized or circulating cytokine. It was originally thought that cleaved TNF-α was the major biological active form, but membrane-expressed TNF-α is biologically active. Researchers in Denmark now report that bioactive TACE is expressed in normal colon mucosa by mononuclear and epithelial cells. However, TACE activity is increased in mucosal biopsies from patients with active ulcerative colitis, raising speculation that TACE might be a new therapeutic target in IBD. Gut (2002) 51, 37–43 SW

The Enteric Nervous System in Intestinal Inflammation

Since about the 1950s nerves in the wall of the intestine have been postulated to play a role in the pathogenesis of inflammatory bowel disease (IBD). Human and animal studies examining the role of nerves in intestinal inflammation are the focus of this review. Consideration is given to two possible ways that nerves are involved in IBD. First, nerves may play a role in the development or maintenance of inflammation through local release of transmitters. Second, once initiated (by whatever means), the processes of inflammation may disrupt the normal pattern of innervation and the interactions of nerves and their target tissues. Many of the functional disturbances observed in IBD are likely due to an alteration in the enteric nervous system either structurally through disruptions of nerve-target relationships or by modifications of neurotransmitters or their receptors. Finally, it appears that the enteric nervous system may be a potential therapeutic target in IBD and that neuroactive drugs acting locally can represent useful agents in the management of this disease.